1. Field of the Invention
The field of the invention relates generally to engine control systems utilizing fuel vapor purging.
2. Background of the Invention
Engine control systems utilize fuel vapor purging to reduce emissions from the vehicle. In these systems, vapors are inducted into the engine intake manifold, and then into the engine cylinders to be burned.
The inventors herein have developed an engine control methodology that allows efficient engine operation with some of the cylinders inducting air with no injected fuel. However, the inventors have also recognized that if fuel vapors are inducted into the engine manifold, some fuel vapor will enter these non-combusting cylinders and pass to the exhaust unburned. As such, if the exhaust system is at a high temperature, the exhaust system may become too hot. Alternatively, if the exhaust system is not at a high temperature, then vapors may pass through the exhaust unburned, thereby increasing engine emissions.
Various of the above problems can be reduced by operation according to a method having a first and second group of cylinders, operating in a first mode wherein the first cylinder group operates with air and substantially no injected fuel and the second cylinder group operates by combusting air and injected fuel, providing a request for fuel vapor purging, and in response to the request, disabling the first mode of operation and operating the engine in a second mode of operation. By disabling the first mode, it is possible to operate in another mode that can more efficiently burn the inducted fuel vapors.
In another aspect of the present invention, the method comprises combusted air and injected fuel in the second group near stoichiometry.
By allowing fuel vapor purging in said first mode when the exhaust temperature is within a predetermined range, it is possible to react the fuel vapors with excess oxygen over the catalyst. However, if this causes the temperature to move outside the range, the engine can be transitioned to a second mode that allows burning of the fuel vapors with increasing exhaust gas temperature.